The fast development of telecommunications has made it possible for operators to provide users with a multitude of different services. A network architecture providing advanced services is referred to as an Intelligent Network, commonly abbreviated to IN. An intelligent network architecture may be applied to most telecommunication networks, such as the PSTN (Public Switched Telephone Network), PSPDN (Packet Switched Public Data Network, as well as ISDN and B-ISDN networks (Integrated Services Digital Network, Broadband ISDN). Independent of the network architecture, the purpose of intelligent network architecture is to facilitate the creation, control and management of new tele services. Present IN specifications include the Bellcore AIN Rel.1 (Advanced Intelligent Network, Release 1) and the ITU-T (formerly, CCITT) specification Capability Set 1 (CS-1).
The functional architecture of an intelligent network is illustrated by FIG. 1, in which the functional entities of the network are presented as ovals. In the following, a brief discussion will be offered of this architecture in order to make the method according to the invention easier to understand.
The end user's (subscriber's) access to the network is handled by a CCAF function (Call Control Agent Function). Access to IN services is implemented by making amendments to the existing digital exchanges. This is carried out by utilizing a BCSM (Basic Call State Model) which describes the existing functionality by which a call between two users is processed. The BCSM is a high-layer state automaton description of the CCF functions (Call Control Function) required for setting up and maintaining an inter-user connection route. By means of an SSF function (Service Switching Function), functionality is incorporated into this state model (cf. the partly overlapping elements CCF and SSF in FIG. 1), to be able to decide when services of the intelligent network (i.e. IN services) must be invoked. When these IN services have been invoked, a Service Control Function (SCF) containing the service logic of the intelligent network takes care of the service-specific handling (of a call attempt). The SSF, then, couples the CCF (Call Control Function) to the SCF (Service Control Function) and allows it to control the CCF. The SCF may e.g. request the SSF/CCF to carry out particular call or connection functions, for example charging or routing operations. The SCF may also send requests to an SDF (Service Data Function) which handles access to service-specific information and network information of the intelligent network. Thus, the SCF may e.g. request the SDF to retrieve information on a specific service or to update such information. The SDF conceals the actual implementation of the information from the SCF and offers the SCF a logical view of the information.
The operations described above are further complemented by an SRF (Specialized Resources Function), which provides specialized measures required to carry out some services offered by the intelligent network. These include protocol changes, speech recognition, voice announcements, etc. The SCF may e.g. request the SSF/CCF functions to first establish a connection between the end users and the SRF, and then request the SRF to give voice messages to the end users.
Other functional entities of the intelligent network are various kinds of management-related operations, such as SCEF (Service Creation Environment Function), SMF (Service Management Function), and SMAF (Service Management Access Function). The SMF comprises e.g. the management of services, the SMAF provides an interface to the SMF, and the SCEF enables defining, development, testing and inputting to the SMF of the IN services. As these functions are only related to the operation of the network operator, they are not shown in FIG. 1.
In the following, the role of the functional entities illustrated by FIG. 1 will be briefly described from the point of view of the IN services. The CCAF receives a service request sent by a calling party, the service request typically consisting of an offhook and/or a specific series of digits dialled by the calling party. The CCAF forwards the service request to the CCF/SSF for processing. The call control function CCF has no service information but it has been programmed to recognize service requests. The CCF interrupts call setup for a moment and informs the service switching function SSF of the call state. By utilizing predetermined criteria, the task of the SSF is to interrupt the service request, and consequently to determine whether the service request is one relating to IN services. If that is the case, the SSF forms a standardized IN service request and sends the request, with the information on the state of the service request, to the SCF. The SCF receives the request and decodes it. Following this, the SCF cooperates with the SSF/CCF, SRF and SDF to provide the end user with the service requested.
The architecture of the IN physical layer illustrates how the functional entities described above are mapped to the physical entities of the network. The physical architecture of the intelligent network is illustrated in FIG. 2, in which the physical entities are depicted as rectangles or circles and the functional entities as ovals. Signalling links are illustrated by broken lines and the actual transport, such as speech, by solid lines. Optional functional entities are marked with a broken line. The signalling network illustrated by the figure is a network in accordance with Signalling System Number 7 (SS7 is a prior art signalling system, described in the CCITT (nowadays ITU-T) Blue Book Specifications of Signalling System No. 7, Melbourne, 1988).
Subscriber equipments SE, e.g. a phone, computer or telefax, are coupled to the SSP (Service Switching Point) directly, or a NAP (Network Access Point).
The service switching point SSP provides a user with access to the network and handles all necessary selection functions. The SSP is also capable of detecting service requests by the intelligent network. Functionally, the SSP comprises call control and service selection features.
The network access point NAP is a conventional switching exchange, such as the applicant's DX 220, containing the CCF function and capable of distinguishing calls that require IN services from ordinary calls, and of routing the calls requiring IN services to the relevant SSP.
An SCP (Service Control Point) includes the service programs that are used for producing IN services.
An SDP (Service Data Point) is a database containing customer and network data which are used by the SCP service programs for producing specialized services. The SCP may employ the services of the SDP directly or via a signalling network.
An IP (Intelligent Peripheral) provides special features, such as announcements and dual tone multifrequency (DTMF) detection.
An SSCP (Service Switching and Control Point) consists of an SCP and SSP in one node (i.e. if the SSP node of FIG. 2 contains both the SCF and the SDF entities, an SSCP is in question).
The tasks of an SMP (Service Management Point) include management of the database (SDP), network monitoring and testing, and gathering of network data. It may connect to all other physical entities.
An SCEP (Service Creation Environment Point) is employed for determining, developing and testing of IN services, and inputting the services to the SMP.
An adjunct (AD) is functionally equivalent to a service control point SCP but it is directly connected to a SSP by a high-speed data link (e.g. ISDN 30B+D interface) and not via an SS No. 7 network.
An SN (Service Node) may control the IN services and carry out data transfer with the users. It communicates with one or more SSPs directly.
An SMAP (Service Management Access Point) is a physical entity offering a connection to the SMP for specific users.
In the above, an intelligent network has been outlined as a background to describing the method according to the invention. A reader interested in the topic may obtain a more thorough understanding of an intelligent network from e.g. ITU-T recommendations Q.121X or Bellcore AIN recommendations.
To facilitate comprehending the method according to the invention, a call state model, referred to in the above, will be described. The components illustrating the model are PIC (Points In Call), DP (Detection Points), transitions and events. The PICs identify those CCF functions that are required to complete one or more call/connection states. The DPs detect the points in the calling and connection process at which transfer of control to the IN may take place. (Next to the DPs there is a name referring to them; in the ETSI (European Telecommunications Standard Institute) standards the names relate to the DPs themselves, whereas in the ITU-T standards the names are associated with the messages transmitted by the SSF to the SCF from the DP in question.) The transitions indicate a normal flow of a call/connection process from a PIC to another. Events cause transitions into and from the PIC. A thorough description will not be given here; for a detailed description, reference is made to the recommendation Q.1214. In the following, the PICs are briefly described.
FIG. 3 shows an O.sub.-- BCSM (Originating Basic Call State Model) according to recommendation Q.1214. A PIC 1 (0.sub.-- Null & Authorize.sub.-- Origination.sub.-- Attempt) input event is disconnecting the previous connection (DP 9 or DP 10). The function is to set the interface to idle mode and to check the authority of the calling party (the calling party's authority to carry out a call with given properties is checked). At PIC 2, initial information is gathered from the calling party. Such information includes e.g. service codes and dialled address digits. At PIC 3, the information obtained is analyzed to determine a routing address and call type (e.g. a local exchange call/transit exchange call/international exchange call). At PIC 4, e.g. routing of the call is carried out. An initiation information is transmitted to the terminating half BCSM model, and call control is transferred to the terminating half. The entry event of PIC 5 is constituted by an indication from the terminating half BCSM that the call has been answered by the called party. The function is establishment of connection between calling and called parties, and collection of charging data. Exit events are a service request from the calling party (DP 8), information on that either the calling or called party has disconnected the call (DP 9), or occurrence of a connection failure (transition to PIC 6). At PIC 6, default and exception conditions are handled.
FIG. 4 illustrates a T.sub.-- BCSM (Terminating Basic Call State Model) according to the recommendation Q.1214. The entry event of PIC 7 is disconnecting and clearing of a previous call (DP 17 or DP 18), or default handling of exceptions by SSF/CCF completed (PIC 11). The function is to set the interface to idle state, and verification of authority (authority to route the call to the called party). At PIC 8, the available resource is selected, and the called party is informed of the incoming call. The exit events are alerting the terminating party (transition to PIC 9), available resources or the called party being busy (DP 13), the call being answered by the called party (DP 15), or the calling party abandoning the call (DP 18). At PIC 9, an indication is sent to the originating half BCSM that the called party is being alerted, and an answer by the called party to the call is awaited. The exit events are that the called party does not answer within a specified time period (DP 14), the called party answers the call (DP 15), or the calling party abandons the call (DP 18). A transition to PIC 10 takes place when the called party answers the call. At PIC 10, an indication is sent to the originating half BCSM that the called party has answered the call, and a connection is established between the calling and the called parties. The exit events are: a service request is received from the called party (DP 16), a disconnect indication is received from either the calling or the called party (DP 17), or a failure occurs (transition to PIC 11). At PIC 11, default and exception conditions are handled.
A large number of various kinds of services may be offered in an intelligent network, such as ABD (Abbreviated Dialing), AAB (Automatic Alternative Billing), and CF (Call Forwarding). The services cannot, however, be implemented in a versatile manner from the point of view of the called party (B subscriber), but they are for the most part services for the calling party (A subscriber). This results from the fact that possibilities to control a service are much more many-sided in the originating half BCSM. (As also indicated by FIGS. 3 and 4, interception of calls and charging related thereto, gathering data from a user and release and completion of a call attempt and continuation, among other things, are possible in a versatile manner only according to the originating half BCSM.)